This invention relates to a process for preparing aqueous dispersions of rosin-base materials, and more particularly to a process for preparing aqueous dispersed size of lowered surfactant requirement and tendency to foam.
Cellulose fiber products such as paper and paperboards are produced from an aqueous slurry of cellulose fibers containing sizing agents admixed therewith. These sizing agents generally comprise aqueous dispersions of rosin, especially fortified rosin, which is utilized to modify the surface of the paper to control water penetration.
The present invention relates to a process for improving the properties of dispersed rosins size produced by the inversion method wherein a dispersant and water are mixed together to form a dispersion and are added to a molten rosin-base material to form a dispersion comprising a continuous phase of the rosin and a dispersed phase of the water, and to the dispersion water is added to invert the dispersion to the contemplated aqueous dispersion comprising a dispersed phase of the rosin and a continuous phase of the water.
Attention is directed to the disclosure of related U.S. Pat. Nos. 4,267,099 and 4,309,338 to Okumichi et al for an in depth discussion of a method of preparing a dispersed rosin size by the inversion method.
Okumichi et al provide a process for preparing an aqueous dispersion of a rosin-base material by the inversion method characterized by reduced foaming properties achieved by use of at least one of the dispersants disclosed and claimed therein. While dispersed rosin size prepared in accordance with Okumichi et al and particularly sizes produced with a dispersant selected from the salts of sulfuric acid half ester of the formula II, referred to by Okumichi et al as "sulfates" provides dispersed rosin size of reduced foaming properties the size still tended to produce excessive foam under conditions normally encountered in some paper making machines.
Okumichi et al thus approached the problem of lowering the tendency of a dispersed rosin sized foam by specifically tailoring the dispersant, or surfactant, albeit they do recognize the obvious expedient of lowering the surfactant level in the size to lower the tendency of the size to foam. Unfortunately, a simple lowering of surfactant level is not practicable because surfactant level is tied to the very ability to produce a dispersion.
Kawatani et al, see Japanese Kokai No. 79 58,759 comprises a disclosure that is representative of another approach to lowering the tendency of aqueous rosin dispersions to foam through the use of internal foam depressors. Kawatani et al teach the use of simple aliphatic acids, e.g., caproic, caprylic, lauric, or myristic, for this purpose. This method of foam lowering is unappealing because the amount of rosin available for sizing is reduced, contaminates with unknown effects are introduced, and the basic problem of inefficient surfactant usage is neglected.